Strap-cell architecture for embedded memory

ABSTRACT

Various embodiments of the present application are directed towards an integrated memory chip comprising a memory array with a strap-cell architecture that reduces the number of distinct strap-cell types and that reduces strap-line density. In some embodiments, the memory array is limited to three distinct types of strap cells: a source line/erase gate (SLEG) strap cell; a control gate/word line (CGWL) strap cell; and a word-line strap cell. The small number of distinct strap-cell types simplifies design of the memory array and further simplifies design of a corresponding interconnect structure. Further, in some embodiments, the three distinct strap-cell types electrically couple word lines, erase gates, and control gates to corresponding strap lines in different metallization layers of an interconnect structure. By spreading the strap lines amongst different metallization layers, strap-line density is reduced.

REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Application No.62/737,274, filed on Sep. 27, 2018, the contents of which are herebyincorporated by reference in their entirety.

BACKGROUND

Embedded flash is flash memory that is integrated with logic devices ona common integrated circuit (IC) chip. The integration improvesperformance by eliminating interconnect structures between chips andreduces manufacturing costs by sharing process steps between the flashmemory and the logic devices. Some types of flash memory include stackedgate flash memory and split gate flash memory. Split gate flash memoryhas lower power consumption, higher injection efficiency, lesssusceptibility to short channel effects, and over erase immunitycompared to stacked gate flash memory.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 illustrates a schematic diagram of some embodiments of anintegrated chip comprising a memory array with an enhanced strap-cellarchitecture and further comprising an interconnect structurecorresponding to the enhanced strap-cell architecture.

FIG. 2 illustrates a block diagram of some embodiments of an integratedchip comprising a memory array with the enhanced strap-cell architectureof FIG. 1.

FIG. 3 illustrates a block diagram of some embodiments of an integratedchip comprising a memory array with the enhanced strap-cell architectureof FIG. 1 and further comprising peripheral devices surrounding thememory array.

FIGS. 4A and 4B illustrate top layouts of some embodiments of integratedchips comprising a boundary cell of FIG. 1, a source-line/erase-gate(SLEG) strap cell of FIG. 1, and memory cells of FIG. 1.

FIGS. 5A-5C illustrate cross-sectional views of some embodiments of theintegrated chip of FIG. 4A or 4B respectively at the boundary cell, theSLEG strap cell, and the memory cell.

FIGS. 6A and 6B illustrate top layouts of some embodiments of integratedchips comprising a control-gate/word-line (CGWL) strap cell of FIG. 1and memory cells of FIG. 1.

FIGS. 7A and 7B illustrate cross-sectional views of some embodimentsrespectively of the integrated chips of FIGS. 6A and 6B at the CGWLstrap cell.

FIGS. 8A and 8B illustrate top layouts of some embodiments of integratedchips comprising a word-line strap cell of FIG. 1 and memory cells ofFIG. 1.

FIGS. 9A and 9B illustrate cross-sectional views of some embodimentsrespectively of the integrated chips of FIGS. 8A and 8B at the word-linestrap cell.

FIGS. 10A-10F illustrate top layouts of some embodiments of theintegrated chip of FIG. 1 respectively at different levels of theintegrated chip and in which the memory array comprises additionalcolumns.

FIGS. 11A-11D through FIGS. 20A-20D illustrate a series ofcross-sectional views of some embodiments of a method for forming anintegrated chip comprising a memory array with an enhanced strap-cellarchitecture.

FIG. 21 illustrates a block diagram of some embodiments of the method ofFIGS. 11A-11D through FIGS. 20A-20D.

DETAILED DESCRIPTION

The present disclosure provides many different embodiments, or examples,for implementing different features of this disclosure. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

In some embodiments, a memory array comprises multiple split-gate memorycells in multiple rows and multiple columns, and further comprisesmultiple polysilicon lines and multiple buried lines extending along therows. The polysilicon and buried lines partially define the split-gatememory cells and facilitate reading from and/or writing to thesplit-gate memory cells. The polysilicon lines may, for example,correspond to control gates, word lines, and erase gates, and the buriedlines may, for example, correspond to source lines. A challenge is thatthat the polysilicon and buried lines have high resistances that lead tolarge voltage drops along the polysilicon and buried lines. Such largevoltage drops increase minimum read and/or write voltage and hencereduce power efficiency. A solution is to strap metal lines to thepolysilicon and buried lines since the metal lines have lowerresistances. Hence, some embodiments of the memory array comprise strapcells spaced along the polysilicon and buried lines for use as locationsto electrically couple the metal lines to the polysilicon and buriedlines.

In some embodiments, the memory array comprises four distinct types ofstrap cells: a control gate/source line (CGSL) strap cell; a source line(SL) strap cell; a word line/erase gate (WLEG) strap cell; and an erasegate (EG) strap cell. However, the large number of distinct types ofstrap cells leads to complexity when designing the memory array.Additionally, in some embodiments, the metal lines for the word lines,the erase gates, and the control gates are in a single metallizationlayer (e.g., metal 3) of an interconnect structure. However, arrangingthe metal lines for the word lines, the erase gates, and the controlgates in a single metallization layer may pose challenges as the memoryarray shrinks (e.g., to process node 40 and beyond). For example, as thememory array shrinks, extreme low k (ELK) dielectric materials may beused for inter-metal and/or inter-layer dielectric layers of theinterconnect structure. However, ELK dielectric materials tend to havehigh porosity and hence low time dependent dielectric breakdowns (TDDBs)compared to their non-porous counterparts with higher dielectricconstants. Due to the low TDDBs, the minimum spacing between metal linesis higher than when using the non-porous counterparts. Further, due tothe large number of metal lines in a single metallization layer,meaningful scaling of the memory array is precluded without violatingthe minimum spacing constraint. To violate this constraint potentiallyleads to device failure and/or a high amount of leakage current betweenmetal lines.

Various embodiments of the present application are directed towards anintegrated memory chip comprising a memory array with a strap-cellarchitecture that reduces the number of distinct strap-cell types andthat reduces strap-line density. In some embodiments, the memory arrayis limited to three distinct types of strap cells: a source line/erasegate (SLEG) strap cell; a control gate/word line (CGWL) strap cell; anda word-line strap cell. The small number of distinct strap-cell typessimplifies design of the memory array and further simplifies design of acorresponding interconnect structure.

The three distinct strap-cell types may, for example, electricallycouple word lines, erase gates, and control gates to corresponding straplines in different metallization layers of an interconnect structure.For example, the word lines may be electrically coupled to word-linestrap lines in metal 2, the control gates may be electrically coupled tocontrol-gate strap lines in metal 3, and the erase gates may beelectrically coupled to erase-gate strap lines in metal 4. Othersuitable metallization layers are, however, amenable for the word-linestrap lines, the control-gate strap lines, and the erase-gate straplines. By spreading the word-line strap lines, the control-gate straplines, and the erase-gate strap lines amongst different metallizationlayers, strap-line density is reduced (i.e., strap-line spacing isincreased). This allows enhanced scaling of the memory array (e.g., toprocess node 40 and beyond) and/or allows use of ELK dielectricmaterials for inter-layer and/or inter-metal dielectric layers of theinterconnect structure.

The three distinct strap-cell types may, for example, be laid out toprovide electrical coupling to corresponding strap lines at frequenciesthat minimize read and/or write voltage drops and/or that matchstrap-cell architectures with four or more distinct strap-cell types (anexample of which is noted above). For example, SLEG strap cells mayelectrically couple a source line to a corresponding source-line strapline with a first frequency, and CGWL strap cells and word-line strapcells may electrically couple a word line to a corresponding word-linestrap line at a second frequency, to prevent large read voltage dropsalong the source line and the word line. The first frequency may, forexample, be 32 bit lines or some other suitable value. The secondfrequency may, for example, be twice the first frequency or some othersuitable multiple and/or may, for example, be 64 bit lines or some othersuitable value.

With reference to FIG. 1, a schematic diagram 100 of some embodiments ofan integrated chip comprising a memory array with an enhanced strap-cellarchitecture is provided. As seen hereafter, the enhanced strap-cellarchitecture is “enhanced” in that it reduces the number of distinctstrap-cell types and reduces strap-line density. The memory arraycomprises a plurality of cells in a plurality of rows and a plurality ofcolumns. The rows are respectively labeled R₁ through R_(l+7) and thecolumns are respectively labeled C₁ through C₃, C_(n) through C_(n+2),and C_(o) through C_(o+1). The subscripts of the row and column labelsidentify corresponding row and column numbers. Further, 1 is an integervariable representing a row number whereas n and o are integer variablesrepresenting column numbers.

The plurality of cells comprises a plurality of boundary cells 102, aplurality of SLEG strap cells 104, a plurality of CGWL strap cells 106,a plurality of word-line strap cells 108, and a plurality of memorycells 110. Note that only some of each type of cell are labeled. Theboundary cells 102 are unused cells at a boundary of a memory array andeach span two rows. The boundary cells 102 offset the memory and strapcells from the boundary to protect the memory and strap cells from alarge change in feature density, and hence a high degree of processnon-uniformity, at the boundary. The SLEG strap cells 104, the CGWLstrap cells 106, and the word-line strap cells 108 each span two rowsand, although not visible, repeat along each of the rows. The SLEG strapcells 104 electrically couple source lines (not shown) and erase gates(not shown) to a corresponding source-line strap line 112 and acorresponding erase-gate strap line 114. The CGWL strap cells 106electrically couple control gates (not shown) and word lines (not shown)to corresponding control-gate strap lines 116 and correspondingword-line strap lines 118. The word-line strap cells 108 electricallycouple the word lines to corresponding word-line strap lines 118. Notethat only some of the control-gate strap lines 116 and only some of theword-line strap lines 118 are labeled. The control gates, the wordlines, the erase gates, and the source lines extend along the rows andpartially define the plurality of cells. The memory cells 110 storeindividual bits of data and may, for example, be third generationSUPERFLASH (ESF3) memory cells or some other suitable memory cells.

In some embodiments, the memory array is limited to the three distincttypes of strap cells: 1) the SLEG strap cells 104; 2) the CGWL strapcells 106; and 3) the word-line strap cells 108. This small number ofdistinct strap-cell types simplifies design of the memory array comparedto a memory array with four or more distinct strap-cell types, andfurther simplifies design of an interconnect structure for the memoryarray compared to an interconnect structure for a memory array with fouror more distinct strap-cell types.

An interconnect structure interconnects the plurality of cells andcomprises a plurality of wires 120 and a plurality of vias 122. Notethat the wires 120 and the vias 122 are only labeled in the legend belowthe memory array. The wires 120 are grouped into a plurality of wirelevels and the vias 122 are grouped into a plurality of via levels. Alevel corresponds to an elevation above the memory array when theintegrated chip is viewed in cross section. The plurality of wire levelscomprises a first wire level M1, a second wire level M2, a third wirelevel M3, and a fourth wire level M4. The wire levels are schematicallyillustrated by thicknesses of the wires 120 and elevation above thememory array increases with wire thickness. The plurality of via levelscomprises a contact via level CO (i.e., a zero via level), a first vialevel V1, a second via level V2, and a third via level V3. The vialevels are schematically illustrated by shape and/or color. For example,a black circle corresponds to vias in the contact via level CO, whereasa white square corresponds to vias in the second via level V2.

Vias in the contact via level CO extend from the cells to wires in thefirst wire level M1, and vias in the first via level V1 extend fromwires in the first wire level M1 to wires in the second wire level M2.Further, vias in the second via level V2 extend from wires in the secondwire level M2 to wires in the third wire level M3, and vias in the thirdvia level V3 extend from wires in the third wire level M3 to wires inthe fourth wire level M4. Note that where vias at different levelsdirectly overlap, the intervening wires are not shown.

The plurality of wires 120 comprises a plurality of bit lines 124, asource-line shunt wire 126, and an erase-gate shunt wire 128 in thefirst wire level M1. Note that only some of the bit lines 124 arelabeled. The bit lines 124 extend along columns (e.g., columns C₃,C_(n), C_(n+2), and C_(o)) at which the memory cells 110 are located andelectrically couple to memory cells in corresponding columns throughvias in the contact via level CO. The source-line and erase-gate shuntwires 126, 128 extend along the column (e.g., column C₂) at which theSLEG strap cells 104 are located and electrically couple respectively tosource lines (not shown) and erase gates (not shown) at the SLEG strapcells 104 through vias in the contact via level CO.

Additionally, the plurality of wires 120 comprises the source-line strapline 112, the erase-gate strap line 114, the control-gate strap lines116, and the word-line strap lines 118. The source-line and erase-gatestrap lines 112, 114 are in the fourth wire level M4 and electricallycouple respectively to the source-line and erase-gate shunt wires 126,128 through vias in the first, second, and third via levels V1, V2, andV3. The control-gate strap lines 116 are in the third wire level M3 andelectrically couple to control gates (not shown) in corresponding rowsat the CGWL strap cells 106. Such electrical coupling is through vias inthe contact via level CO and the first and second via levels V1, V2. Theword-line strap lines 118 are in the second wire level M2 andelectrically couple to word lines (not shown) in corresponding rows atthe CGWL strap cells 106 and the word-line strap cells 108. Suchelectrical coupling is through vias in the contact via level CO and thefirst via level V1.

By arranging the erase-gate strap line 114, the control-gate strap lines116, and the word-line strap lines 118 in different wire levels (e.g.,M2, M3, and M4), instead of in a single wire level (e.g., M3),strap-line density is reduced (i.e., strap-line spacing is increased)for the various strap lines. Additionally, by reducing strap-linedensity, the memory array may be scaled down for process node 40 andbeyond.

In some embodiments, spacing between strap lines decreases as the memoryarray scales down. Without the reduced strap-line density, the spacingbetween the strap lines may become less than the minimum spacing toprevent TDDB. Further, in some embodiments, ELK dielectric materials areused for inter-metal dielectric (IMD) layers as the memory array scalesdown. ELK dielectric materials tend to have high porosity and hence lowTDDBs compared to their non-porous counterparts with higher dielectricconstants. Due to the low TDDBs, the minimum spacing between strap linesis higher than when using the non-porous counterparts. Hence, use of ELKdielectric materials for IMD layers exacerbates the risk of TDDB andincreases the importance of the reduced strap-line density.

While FIG. 1 illustrates the various strap lines and the various shuntwires as being in certain wire levels, some or all of the strap linesand/or some or all of the shunt wires may be in different wire levels inalternative embodiments. For example, the control-gate strap lines 116may be in the second wire level M2 and the word-line strap lines 118 maybe in the third wire level M3 in alternative embodiments. As anotherexample, the erase-gate strap line 114 may be in the fourth wire levelM4 and the source-line strap line 112 may be in a fifth wire level (notshown), or vice versa, in alternative embodiments.

With reference to FIG. 2, a block diagram 200 of some embodiments of anintegrated chip comprising a memory array with the enhanced strap-cellarchitecture of FIG. 1 is provided. The memory array comprises aplurality of cells in a plurality of rows and a plurality of columns.The rows are respectively labeled R_(m) through R_(m+15) and the columnsare respectively labeled C₁ through C₂₈₇. The subscripts of the row andcolumn labels identify corresponding row and column numbers, and m is aninteger variable representing a row number.

The plurality of cells comprises a plurality of memory-cell blocks 202.Note that only some of the memory-cell blocks 202 are labeled. Each ofthe memory-cell blocks 202 comprises a plurality of memory cells and hasthe same number of memory cells. The memory cells of each memory-cellblock correspond to individual columns in the memory array, such thateach of the memory-cell blocks 202 spans a plurality of columns. In someembodiments, as illustrated, each of the memory-cell blocks 202 hassixteen memory cells spanning sixteen columns. In alternativeembodiments, each of the memory-cell blocks 202 has some other suitablenumber of memory cells spanning some other suitable number of columns.The memory cells of the memory-cell blocks 202 may, for example, be asthe memory cells 110 of FIG. 1 are illustrated and/or described. In someembodiments, the memory-cell blocks 202 are at columns C₃₋₁₈, C₂₀₋₃₅,C₃₇₋₆₈, C₇₀₋₈₅, C₈₇₋₁₀₂, C₁₀₄₋₁₃₅, C₁₃₇₋₁₅₂, C₁₅₄₋₁₆₉, C₁₇₁₋₂₀₂,C₂₀₄₋₂₁₉, C₂₂₁₋₂₃₆, C₂₃₈₋₂₆₉, and C₂₇₁₋₂₈₆. Other columns are, however,amenable.

The plurality of cells further comprises the boundary cells 102 of FIG.1, the plurality of SLEG strap cells 104 of FIG. 1, the plurality ofCGWL strap cells 106 of FIG. 1, and the plurality of word-line strapcells 108 of FIG. 1. Note that only some of the boundary cells 102 arelabeled and only some of each strap-cell type are labeled. As discussedin FIG. 1, the boundary cells 102 are unused cells at a boundary (e.g.,column CO of a memory array and each span two rows. Further, the SLEGstrap cells 104, the CGWL strap cells 106, and the word-line strap cells108 each span two rows and repeat along the rows.

In some embodiments, the SLEG strap cells 104 are at columns C₂, C₃₆,C₆₉, C₁₀₃, C₁₃₆, C₁₇₀, C₂₀₃, C₂₃₇, and C₂₇₀. Other columns are, however,amenable. In some embodiments, the SLEG strap cells 104 are evenlyspaced along the rows and/or repeat periodically along the rows with aSLEG frequency F_(sleg). The SLEG frequency F_(sleg) may, for example,be 32 memory cells (i.e., 32 bit lines) or some other suitable number ofmemory cells and/or bit lines. Further, the SLEG frequency F_(sleg) may,for example, be two memory-cell blocks or some other suitable integernumber of memory-cell blocks. In some embodiments, the SLEG frequencyF_(sleg) is 32 memory cells (i.e., 32 bit lines) or less so source linesare electrically coupled to corresponding source-line strap lines every32 memory cells or less. By electrically coupling the source lines tocorresponding source-line strap lines every 32 memory cells or less,voltage drops along the source lines are small. If the frequency atwhich source lines are electrically couple to corresponding source-linestrap lines is more than 32 memory cells, voltage drops along thesource-line strap lines may be large and may lead to read disturbanceand/or failure.

In some embodiments, the CGWL strap cells 106 are at columns C₁₉, C₁₅₃,and C₂₈₇. Other columns are, however, amenable. In some embodiments, theCGWL strap cells 106 are evenly spaced along the rows and/or repeatperiodically along the rows with a CGWL frequency F_(cgwl). The CGWLfrequency F_(cgwl) may, for example, be 128 memory cells (i.e., 128 bitlines) or some other suitable number of memory cells and/or bit lines.Further, the CGWL frequency F_(cgwl) may, for example, be eightmemory-cell blocks or some other suitable integer number of memory-cellblocks and/or may, for example, be four times the SLEG frequencyF_(sleg) or some other suitable integer multiple of the SLEG frequencyF_(sleg).

In some embodiments, the word-line strap cells 108 are at columns C₈₆and C₂₂₀. Other columns are, however, amenable. In some embodiments, theword-line strap cells 108 are evenly spaced along the rows and/or repeatperiodically along the rows with a word-line frequency F_(wl). Theword-line frequency F_(wl) may, for example, be 128 memory cells (i.e.,128 bit lines) or some other suitable number of memory cells and/or bitlines. Further, the word-line frequency F_(wl) may, for example, beeight memory-cell blocks or some other suitable integer number ofmemory-cell blocks and/or may, for example, be four times that of theSLEG frequency F_(sleg) or some other suitable integer multiple of theSLEG frequency F_(sleg). Further, the word-line frequency F_(wl) may,for example, be the same as the CGWL frequency F_(cgwl).

In some embodiments, the CGWL strap cells 106 and the word-line strapcells 108 alternate and repeat along the rows so word lines areelectrically coupled to corresponding word-line strap lines every 64memory cells (i.e., 64 bit lines) or less. By electrically coupling theword lines to corresponding word-line strap lines every 64 memory cellsor less, voltage drops along the word lines are small. If the frequencyat which word lines are electrically couple to corresponding word-linestrap lines is more than 64 memory cells, voltage drops along the wordlines may be large and may lead to read disturbance and/or failure.

In some embodiments, a portion of the memory array in box BX1 repeatsalong each of the rows, beginning at the boundary cells 102. In someembodiments, the rows of the memory array are grouped into a pluralityof memory pages. For clarity, the memory pages are respectively labeledP_(z) and P_(z+1), where subscripts identify corresponding page numbersand z is an integer variable representing a page number. In someembodiments, as illustrated, each memory page is a portion of the memoryarray defined by eight consecutive rows. In alternative embodiments,each memory page is defined by one, two, sixteen, or some other suitablenumber of consecutive rows. In some embodiments, a portion of the memoryarray in box BX2 repeats at each of the memory pages and/or theschematic diagram 100 of FIG. 1 is taken within box BX2. As to thelatter, column C_(o+1) of FIG. 1 may, for example, be the same as columnC₈₆ of FIG. 2 and/or row R_(l) of FIG. 1 may, for example, be the sameas row R_(m) of FIG. 2.

While not shown in FIG. 2, an interconnect structure interconnects theplurality of cells and comprises a plurality of word-line strap lines, aplurality of control-gate strap lines, a plurality of erase-gate straplines, and a plurality of source-line strap lines. Each row has anindividual word-line strap line extending along the row and further hasan individual control-gate strap line extending along the row. Eachmemory page has an individual erase-gate strap line shared by first rowsof the memory page and extending along the first rows. Similarly, eachmemory page has an individual source-line strap line shared by secondrows of the memory page and extending along the second rows. Theword-line strap lines, the control-gate strap lines, the erase-gatestrap lines, and the source-line strap lines may, for example, be astheir counterparts are described and/or illustrated with regard to FIG.1.

The interconnect structure further comprises a plurality of source-lineshunt wires and a plurality of erase-gate shunt wires. Each memory pagehas a plurality of individual source-line shunt wires, and each memorypage has a plurality of individual erase-gate shunt wires. Theindividual source-line shunt wires of each memory page are respectivelyat the columns with SLEG strap cells 104, and the individual erase-gateshunt wires of each memory page are respectively at the columns withSLEG strap cells 104. The source-line shunt wires and the erase-gateshunt wires may, for example, be as their counterparts are describedand/or illustrated with regard to FIG. 1.

With reference to FIG. 3, a block diagram 300 of some embodiments of anintegrated chip comprising a memory array with the enhanced strap-cellarchitecture of FIG. 1, and further comprising peripheral devices 302surrounding the memory array, is provided. The memory array is at amemory region 304 of the integrated chip and comprises the boundarycells 102 of FIG. 1, the SLEG strap cells 104 of FIG. 1, the CGWL strapcells 106 of FIG. 1, and the word-line strap cells 108 of FIG. 1.Further, the memory array comprises the memory-cell blocks 202 of FIG.2. Note that only some of the boundary cells 102 are labeled, only someof the memory-cell blocks 202 are labeled, and only some of eachstrap-cell type are labeled. In some embodiments, the schematic diagram100 of FIG. 1 is taken within box BX3.

The peripheral devices 302 are at a peripheral region 306 of theintegrated chip that surrounds the memory region 304. Note that onlysome of the peripheral devices 302 are labeled. The peripheral devices302 may, for example, be or comprise transistors and/or some othersuitable semiconductor device(s). Further, the peripheral devices 302may, for example, implement read/write circuitry and/or some othersuitable circuitry for operation of the memory array. By integrating theperipheral devices 302 and the memory array on a common integrated chip,the memory array may also be known as an embedded memory array.

With reference to FIG. 4A, a top layout 400A of some embodiments of anintegrated chip comprising a boundary cell 102 of FIG. 1, a SLEG strapcell 104 of FIG. 1, and memory cells 110 of FIG. 1 is provided. Theboundary cell 102, the SLEG strap cell 104, and the memory cells 110 areon an erase-gate-side device region 402 a and a plurality ofword-line-side device regions 402 b. Note that only some of theword-line-side device regions 402 b is labeled. Further, the boundarycell 102, the SLEG strap cell 104, and the memory cells 110 are definedin part by a pair of word lines 404, a pair of control gates 406, and anerase gate 408.

The erase-gate-side and word-line-side device regions 402 a, 402 bcorrespond to top regions of a substrate 402 (when viewed in crosssection) that are surrounded and demarcated by an isolation structure410. The erase-gate-side device region 402 a is shared by the boundarycell 102, the SLEG strap cell 104, and the memory cells 110. Theword-line-side device regions 402 b are different for the boundary cell102 and the SLEG strap cell 104. The substrate 402 may be or comprise,for example, a bulk monocrystalline silicon substrate, asilicon-on-insulator (SOI) substrate, or some other suitablesemiconductor substrate. The isolation structure 410 may be or comprise,for example, silicon oxide and/or some other suitable dielectricmaterial(s) and/or may be or comprise, for example, a shallow trenchisolation (STI) structure or some other suitable isolation structure.

The word lines 404, the control gates 406, and the erase gate 408 areelongated in parallel along individual lengths L and are spaced fromeach other in a direction perpendicular or otherwise transverse to thelengths L. Note that only one of the lengths L is labeled. The controlgates 406 are between and respectively border the word lines 404, andthe erase gate 408 is between and borders the control gates 406. Incontrast with the word lines 404 and the control gates 406, the erasegate 408 has discontinuities 412 along its length, respectively at theboundary cell 102 and the SLEG strap cell 104. Note that only one of thediscontinuities 412 is labeled. The word lines 404, the control gates406, and the erase gate 408 may be or comprise, for example, dopedpolysilicon and/or some other suitable conductive material(s).

A plurality of vias 122 at the contact via level (i.e., contact vias) ison the SLEG strap cell 104 and the memory cells 110. Note that only someof the vias 122 are labeled. Contact vias at the SLEG strap cell 104electrically couple the erase gate 408 to a corresponding erase-gatestrap line (not shown), and further electrically couple a source line(not shown) underlying the erase gate 408 (when viewed in cross section)to a corresponding source-line strap line (not shown). Contact vias atthe memory cells 110 electrically couple individual source/drain regions(not shown) of the memory cells 110 to a corresponding bit line (notshown).

With reference to FIG. 4B, a top layout 400B of some alternativeembodiments of the integrated chip of FIG. 4A is provided in which theboundary cell 102 and the SLEG strap cell 104 share word-line-sidedevice regions 402 b.

With reference to FIG. 5A, a cross-sectional view 500A of someembodiments of the integrated chip of FIG. 4A and/or FIG. 4B is providedat the boundary cell 102. The cross-sectional view 500A may, forexample, be taken along line A in FIG. 4A and/or FIG. 4B. The word lines404 and the control gates 406 overlie the substrate 402 and theisolation structure 410. Further, the word lines 404 and the controlgates 406 respectively border source/drain regions 502 and a source line504 in the substrate 402. The word lines 404 are between andrespectively border the source/drain regions 502, and the control gates406 are respectively on opposite sides of the source line 504. Note thatonly one of the word lines 404, only one of the control gates 406, andonly one of the source/drain regions 502 are labeled.

The source/drain regions 502 and the source line 504 are doped regionsof the substrate 402. The source/drain regions 502 and the source line504 may, for example, share a doping type (e.g., p-type or n-type)and/or may, for example, have opposite doping types as adjoining regionsof the substrate 402. During operation of the integrated chip,conductive channels (not shown) may form under the word lines 404 andthe control gates 406, along a top surface of the substrate 402. Theisolation structure 410 prevents the conductive channels from extendingfrom the source/drain regions 502 to the source line 504 at the boundarycell 102.

The control gates 406 overlie individual floating gates 506 and arecovered by individual control-gate hard masks 508. The floating gates506 are spaced from the substrate 402 by individual floating-gatedielectric layers 510 and are spaced from the control gates 406 byindividual control-gate dielectric layers 512. Note that only one of thefloating gates 506, only one of the control-gate hard masks 508, onlyone of the floating-gate dielectric layers 510, and only one of thecontrol-gate dielectric layers 512 are labeled. The floating gates 506may be or comprise, for example, doped polysilicon and/or some othersuitable conductive material(s). The floating-gate dielectric layers 510may be or comprise, for example, silicon oxide and/or some othersuitable dielectric(s). The control-gate hard masks 508 and/or thecontrol-gate dielectric layers 512 may be or comprise, for example,silicon oxide, silicon nitride, some other suitable dielectric(s), orany combination of the foregoing.

The control gates 406 are lined by individual control-gate sidewallspacers 514, and the floating gates 506 and the source line 504 arelined by an erase-gate dielectric layer 516. Further, the word lines 404are lined by individual word-line dielectric layers 518. Note that onlyone of the control-gate sidewall spacers 514 and only one of theword-line dielectric layers 518 are labeled. The erase-gate dielectriclayer 516 separates an erase gate (out of view) from the floating gates506, the source line 504, and the control-gate sidewall spacers 514. Theword-line dielectric layers 518 separate the word lines 404 from thecontrol-gate sidewall spacers 514 and the substrate 402. Thecontrol-gate sidewall spacers 514 may be or comprise, for example,silicon oxide, silicon nitride, some other suitable dielectric(s), orany combination of the foregoing. The erase-gate dielectric layer 516and/or the word-line dielectric layers 518 may be or comprise, forexample, silicon oxide and/or some other suitable dielectric(s).

Silicide layers 520 respectively cover the word lines 404 and thesource/drain regions 502, and an interconnect structure 522 covers thesilicide layers 520 and the boundary cell 102. Note that only some ofthe silicide layers 520 are labeled. The silicide layers 520 may, forexample, be or comprise nickel silicide and/or some other suitablesilicide. The interconnect structure 522 comprises an interconnectdielectric layer 524, and further comprises a plurality wires 120 and aplurality of vias (none of which are visible in FIG. 5A) stacked in theinterconnect dielectric layer 524. The interconnect dielectric layer 524may, for example, be or comprises an ELK dielectric material and/or someother suitable dielectric material(s). The ELK dielectric material may,for example, have a dielectric constant less than about 2.5, 2.0, orsome other suitable value and/or may, for example, be or comprise poroussilicon oxycarbide (SiOC) and/or some other suitable ELK dielectricmaterial(s)

The wires 120 are grouped into a first wire level M1, a second wirelevel M2, a third wire level M3, and a fourth wire level M4, whereas thevias are grouped into a contact via level CO, a first via level V1, asecond via level V2, and a third via level V3. At the second wire levelM2, word-line strap lines 118 respectively overlie the word lines 404.The word-line strap lines 118 are electrically coupled to the word lines404 outside of the cross-sectional view 500A of FIG. 5A. At the thirdwire level M3, control-gate strap lines 116 respectively overlie thecontrol gates 406. The control-gate strap lines 116 are electricallycoupled to the control gates 406 outside of the cross-sectional view500A of FIG. 5A. At the fourth wire level M4, an erase-gate strap line114 overlies the boundary cell 102. The erase-gate strap line 114 iselectrically coupled to an erase gate (not shown) outside of thecross-sectional view 500A of FIG. 5A.

The wires 120 and the vias have lower resistances than the word lines404, the control gates 406, the erase gate, and the source line 504.Hence, electrically coupling the various strap lines periodically to theword lines 404, the control gates 406, the source line 504, and erasegate reduces voltage drops therealong. The wires 120 and the vias may beor comprise, for example, copper, aluminum copper, aluminum, tungsten,some other suitable metal(s), some other suitable conductivematerial(s), or any combination of the foregoing. In some embodiments,the word lines 404, the control gates 406, and the erase gate comprisedoped polysilicon and the source line 504 comprises dopedmonocrystalline silicon, whereas the wires 120 and the vias comprisemetal. Other materials are, however, amenable in alternativeembodiments.

With reference to FIG. 5B, a cross-sectional view 500B of someembodiments of the integrated chip of FIG. 4A and/or FIG. 4B is providedat the SLEG strap cell 104. The cross-sectional view 500B may, forexample, be taken along line B in FIG. 4A and/or FIG. 4B. The SLEG strapcell 104 is as the boundary cell 102 of FIG. 5A is illustrated and/ordescribed, except that the source line 504 is electrically coupled to asource-line shunt wire 126 at the first wire level M1.

With reference to FIG. 5C, a cross-sectional view 500C of someembodiments of the integrated chip of FIG. 4A and/or FIG. 4B is providedat the memory cells 110. The cross-sectional view 500C may, for example,be take along line C in FIG. 4A and/or FIG. 4B. The memory cells 110 areas the boundary cell 102 of FIG. 5A is illustrated and/or described witha few exceptions. An erase gate 408 covers the source line 504, and thesilicide layers 520 cover the erase gate 408. Further, the isolationstructure 410 (see FIG. 5A) is removed and the source/drain regions 502are electrically coupled to a bit line 124 at the first wire level M1.Note that only some of the silicide layers 520 and only one of thesource/drain regions 502 are labeled.

By removing the isolation structure 410 from under the memory cells 110,conductive channels (not shown) may form under the memory cells 110,along a top surface of the substrate 402. Such conductive channels mayextend from the source/drain regions 502 to the source line 504 tofacilitate reading and/or writing to the memory cells 110.

With reference to FIG. 6A, a top layout 600A of some embodiments of anintegrated chip comprising a CGWL strap cell 106 of FIG. 1 and memorycells 110 of FIG. 1 is provided. The CGWL strap cell 106 and the memorycells 110 are on an erase-gate-side device region 402 a of a substrate402, a plurality of word-line-side device regions 402 b of the substrate402, and an isolation structure 410. Note that only some of theword-line-side device regions 402 b are labeled. The substrate 402, theerase-gate-side and word-line-side device regions 402 a, 402 b, and theisolation structure 410 may, for example, be as described with regard toFIG. 4A.

A pair of word lines 404, a pair of control gates 406, and an erase gate408 partially define the CGWL strap cell 106 and the memory cells 110.The word lines 404, the control gates 406, and the erase gate 408 may,for example, be as described with regard to FIG. 4A, except that theerase gate 408 is continuous at the CGWL strap cell 106 and the memorycells 110. Further, the control gates 406 have individual pad regions602 at the CGWL strap cell 106. The pad regions 602 are diagonallyopposite and each protrude from a single side of a respective one of thecontrol gates 406 through a neighboring one of the word lines 404. This,in turn, introduces discontinuities along individual lengths of the wordlines 404.

A plurality of vias 122 at the contact via level (i.e., contact vias) ison the CGWL strap cell 106 and the memory cells 110. Note that only someof the vias 122 are labeled. Contact vias at the CGWL strap cell 106electrically couple the pad regions 602 to corresponding control-gatestrap line (not shown), and further electrically couple the word lines404 to corresponding word-line strap lines (not shown). Contact vias atthe memory cells 110 electrically couple individual source/drain regions(not shown) of the memory cells 110 to corresponding bit lines (notshown).

With reference to FIG. 6B, a top layout 600B of some alternativeembodiments of the integrated chip of FIG. 6A is provided in which thepad regions 602 of the control gates 406 each protrude from oppositesides of a respective one of the control gates 406. Further, the erasegate 408 conforms around the pad regions 602 and the word lines 404 arecontinuous at the pad regions 602.

With reference to FIG. 7A, a cross-sectional view 700A of someembodiments of the integrated chip of FIG. 6A is provided at the CGWLstrap cell 106. The cross-sectional view 700A may, for example, be takenalong line D in FIG. 6A. The SLEG strap cell 104 is as the boundary cell102 of FIG. 5A is illustrated and/or described, except that the sourceline 504 is covered by an erase gate 408 and a leftmost one of thecontrol gates 406 has a pad region 602. Further, there is no word linebetween the pad region 602 and a neighboring one of the source/drainregions 502. Note that only one of the control gates 406 and only one ofthe source/drain regions 502 are labeled. The pad region 602 iselectrically coupled to an overlying control-gate strap line 116 throughthe interconnect structure 522.

With reference to FIG. 7B, a cross-sectional view 700B of someembodiments of the integrated chip of FIG. 6B is provided at the CGWLstrap cell 106. The cross-sectional view 700B may, for example, be takenalong line D in FIG. 6B and is variant of FIG. 7A in which a word line404 is between the pad region 602 and a neighboring source/drain region502.

With reference to FIG. 8A, a top layout 800A of some embodiments of anintegrated chip comprising a word-line strap cell 108 of FIG. 1 andmemory cells 110 of FIG. 1 is provided. The word-line strap cell 108 andthe memory cells 110 are on an erase-gate-side device region 402 a of asubstrate 402, a plurality of word-line-side device regions 402 b of thesubstrate 402, and an isolation structure 410. The substrate 402, theerase-gate-side and word-line-side device regions 402 a, 402 b, and theisolation structure 410 may, for example, be as described with regard toFIG. 4A.

A pair of word lines 404, a pair of control gates 406, and an erase gate408 partially define the word-line strap cell 108 and the memory cells110. The word lines 404, the control gates 406, and the erase gate 408may, for example, be as described with regard to FIG. 4A, except thatthe erase gate 408 is continuous at the word-line strap cell 108.

A plurality of vias 122 at the contact via level (i.e., contact vias) ison the word-line strap cell 108 and the memory cells 110. Note that onlysome of the vias 122 are labeled. Contact vias at the word-line strapcell 108 electrically couple the word lines 404 to correspondingword-line strap lines (not shown). Contact vias at the memory cells 110electrically couple individual source/drain regions (not shown) of thememory cells 110 to corresponding bit lines (not shown).

With reference to FIG. 8B, a top layout 800B of some alternativeembodiments of the integrated chip of FIG. 8A is provided in which theword-line-side device regions 402 b are omitted or otherwise integratedwith the erase-gate-side device region 402 a.

With reference to FIG. 9A, a cross-sectional view 900A of someembodiments of the integrated chip of FIG. 8A is provided at theword-line strap cell 108. The cross-sectional view 900A may, forexample, be taken along line E in FIG. 8A. The word-line strap cell 108is as the boundary cell 102 of FIG. 5A is illustrated and/or described,except that the source line 504 is covered by an erase gate 408 and theisolation structure 410 is localized under the word lines 404. Further,the word lines 404 are electrically coupled to corresponding word-linestrap lines 118 in the interconnect structure 522.

With reference to FIG. 9B, a cross-sectional view 900B of someembodiments of the integrated chip of FIG. 8B is provided at theword-line strap cell 108. The cross-sectional view 900B may, forexample, be taken along line E in FIG. 8B and is variant of FIG. 9A inwhich the isolation structure 410 is omitted from under the word-linestrap cell 108.

With reference to FIGS. 10A-10F, top layouts 1000A-1000F of someembodiments of the integrated chip of FIG. 1 respectively at differentlevels of the integrated chip are provided in which the memory arraycomprises additional columns. The additional columns are between columnC_(n+2) and column C_(o) and comprise columns C_(p) through C_(p+2) andcolumns C_(q) through C_(q+2), where n, o, p, and q are integervariables representing column numbers.

Boundary cells 102 repeat along column C₁, and memory cells 110 repeatalong columns C₃, C_(n), C_(n+2), C_(p), C_(p+2), C_(q), C_(q+2), andC_(o). Other columns are, however, amenable. Additionally, note thatonly one boundary cell and only one memory cell are labeled. Theboundary cells 102 may, for example, each have a top layout as shown inFIG. 4A and/or FIG. 4B and/or may, for example, each have across-sectional view as shown in FIG. 5A. For example, FIG. 5A may betaken along line A in FIGS. 10A-10F. The memory cells 110 may, forexample, each have a top layout as shown in any one or combination ofFIGS. 4A, 4B, 6A, 6B, 8A, and 8B and/or may, for example, each have across-sectional view as shown in FIG. 5C. For example, FIG. 5C may, forexample, be taken along line C in FIGS. 10A-10F.

SLEG strap cells 104 repeat along columns C₂, C_(p+1), and C_(q+1), CGWLstrap cells 106 repeat along column C_(n+1), and word-line strap cells108 repeat along column C_(o+1). Other columns are, however, amenable.Additionally, note that only one of each type of cell has been labeledfor readability. The SLEG strap cells 104 may, for example, each have atop layout as shown in FIG. 4A and/or FIG. 4B and/or may, for example,each have a cross-sectional view as shown in FIG. 5B. For example, FIG.5B may be taken along line B in FIGS. 10A-10F. The CGWL strap cells 106may, for example, each have a top layout as shown in FIG. 6A and/or FIG.6B and/or may, for example, each have a cross-sectional view as shown inFIG. 7A and/or FIG. 7B. For example, FIGS. 7A and 7B may be taken alongline D in FIGS. 10A-10F. The word-line strap cells 108 may, for example,each have a top layout as shown in FIG. 8A and/or FIG. 8B and/or may,for example, each have a cross-sectional view as shown in FIG. 9A and/orFIG. 9B. For example, FIGS. 9A and 9B may be taken along line E in FIGS.10A-10F.

With specific reference to the top layout 1000A of FIG. 10A, anerase-gate-side device region 402 a and a plurality of word-line-sidedevice regions 402 b are surrounded and demarcated by an isolationstructure 410. Further, a plurality of source lines 504 and a pluralityof contact vias 122 _(co) (i.e., vias at a contact via level) are on theerase-gate-side device region 402 a and the word-line-side deviceregions 402 b. Note that only some of the word-line-side device regions402 b, only some of the source lines 504, and some of the contact vias122 _(co) are labeled. The source lines 504 are in the erase-gate-sidedevice regions 402 a and are elongated along corresponding rows. Thecontact vias 122 _(co) electrically couple select portions (e.g., thesource lines 504) of the erase-gate-side device regions 402 a, as wellas gate structures (not shown) on the erase-gate-side device region 402a, to corresponding strap and bit lines overlying the erase-gate-sidedevice regions 402 a when viewed in cross section.

With specific reference to the top layout 1000B of FIG. 10B, theisolation structure 410 and the source lines 504 in FIG. 10A areomitted. Further, a plurality of word lines 404, a plurality of controlgates 406, and a plurality of erase gates 408 are on the erase-gate-sidedevice region 402 a and the word-line-side device regions 402 b. Notethat only some of the word lines 404, only some of the control gates406, only some of the erase gates 408, and only some of theword-line-side device regions 402 b are labeled.

The word lines 404, the control gates 406, and the erase gates 408 areelongated in parallel along corresponding rows and partially define thevarious cells (e.g., the CGWL strap cells 106). At the boundary cells102 and the SLEG strap cells 104, the erase gates 408 havediscontinuities along respective lengths. At the CGWL strap cells 106,the control gates 406 have pad regions 602 protruding through the wordlines 404 and introducing discontinuities into the word lines 404. Notethat only one of the pad regions 602 is labeled. The word lines 404, thecontrol gates 406, and the erase gates 408 are electrically coupled tocorresponding strap lines by the contact vias 122 _(co). Further, selectregions of the erase-gate-side device region 402 a are electricallycoupled to corresponding strap and bit lines by the contact vias 122_(co). Note that only some of the contact vias 122 _(co) are labeled.

With specific reference to the top layout 1000C of FIG. 10C, the wordlines 404 of FIG. 10B, the control gates 406 of FIG. 10B, and the erasegates 408 of FIG. 10B are omitted. Further, a plurality of first-levelwires 120 _(m1) and a plurality of first-level vias 122 _(v1) are on theon the erase-gate-side device region 402 a and the word-line-side deviceregions 402 b. Note that only some of the first-level wires 120 _(m1),only some of the first-level vias 122 _(v1), and only some of theword-line-side device regions 402 b are labeled.

The first-level wires 120 _(m1) electrically couple to underlyingstructure (when viewed in cross section) through the contact vias 122_(co) and electrically couple to overlying wires (when viewed in crosssection) through the first-level vias 122 _(v1) The first-level wires120 _(m1) comprise a plurality of source-line shunt wires 126 and aplurality of erase-gate shunt wires 128. Note that only one of thesource-line shunt wires 126 and only one of the erase-gate shunt wires128 are labeled. The source-line and erase-gate shunt wires 126, 128extend along columns at which the SLEG strap cells 104 are located(e.g., column C₂) and repeat along the columns at each memory page (onlyone of which is shown). By repeating along the columns at each memorypage, the source-line and erase-gate shunt wires 126, 128 facilitateelectrical coupling of the source lines 504 of FIG. 10A and the erasegates 408 of FIG. 10B to corresponding source-line strap lines andcorresponding erase-gate strap lines on a memory-page-by-memory-pagebasis.

With specific reference to the top layout 1000D of FIG. 10D, thefirst-level wires 120 _(m1) of FIG. 10C and the contact vias 122 _(co)of FIG. 10C are omitted. Further, a plurality of second-level wires 120_(m2) and a plurality of second-level vias 122 _(v2) are on the on theerase-gate-side device region 402 a and the word-line-side deviceregions 402 b. Note that only some of the second-level wires 120 _(m2),only some of the second-level vias 122 _(v2), and only some of theword-line-side device regions 402 b are labeled.

The second-level wires 120 _(m2) electrically couple to underlying wires(when viewed in cross section) through the first-level vias 122 _(v1)and electrically couple to overlying wires (when viewed in crosssection) through the second-level vias 122 _(v2). The second-level wires120 _(m2) comprise a plurality of word-line strap lines 118. Note thatonly some of the word-line strap lines 118 are labeled. The word-linestrap lines 118 are elongated along corresponding rows and electricallycouple respectively to the word lines 404 of FIG. 10B.

With specific reference to the top layout 1000E of FIG. 10E, thesecond-level wires 120 _(m2) of FIG. 10D and the first-level vias 122_(v1) of FIG. 10D are omitted. Further, a plurality of third-level wires120 _(m3) and a plurality of third-level vias 122 _(v3) are on the onthe erase-gate-side device region 402 a and the word-line-side deviceregions 402 b. Note that only some of the third-level wires 120 _(m3),only some of the third-level vias 122 _(v3), and only some of theword-line-side device regions 402 b are labeled.

The third-level wires 120 _(m3) electrically couple to underlying wires(when viewed in cross section) through the second-level vias 122 _(v2)and electrically couple to overlying wires (when viewed in crosssection) through the third-level vias 122 _(v3) The third-level wires120 _(m3) comprise a plurality of control-gate strap lines 116. Notethat only some of the control-gate strap lines 116 are labeled. Thecontrol-gate strap lines 116 are elongated along corresponding rows andelectrically couple respectively to the control gates 406 of FIG. 10B.

With specific reference to the top layout 1000F of FIG. 10F, thethird-level wires 120 _(m3) of FIG. 10E and the second-level vias 122_(v2) of FIG. 10E are omitted. Further, a plurality of fourth-levelwires 120 _(m4) are on the on the erase-gate-side device region 402 aand the word-line-side device regions 402 b. Note that only some of thefourth-level wires 120 _(m4) are labeled, Further, the word-line-sidedevice regions 402 b are not labeled in FIG. 10F because theword-line-side device regions 402 b are covered by the fourth-levelwires 120 _(m4).

The fourth-level wires 120 _(m4) electrically couple to underlying wires(when viewed in cross section) through the third-level vias 122 _(v3).The fourth-level wires 120 _(m4) comprise a plurality of source-linestrap lines 112 and an erase-gate strap line 114. The source-line straplines 112 are individual to memory pages and electrically couple tocorresponding source-line shunt wires 126 (see FIG. 10C) in theindividual memory pages. Similarly, the erase-gate strap line 114 isindividual to a memory page and electrically couples to correspondingerase-gate shunt wires 128 (see FIG. 10C) in the individual memory page.

With reference to FIGS. 11A-11D through FIGS. 20A-20D, a series ofcross-sectional views, 1100A-1100D through 2000A-2000D, of someembodiments of a method for forming an integrated chip comprising amemory array with an enhanced strap-cell architecture is provided. Themethod may, for example, be used to form the integrated chip(s) from anyone or combination of FIGS. 1-3, 4A, 4B, 5A-5C, 6A, 6B, 7A, 7B, 8A, 8B,9A, 9B, and 10A-10F.

Amongst FIGS. 11A-11D through FIGS. 20A-20D, figures with a suffix of“A” may, for example, correspond to the boundary cells 102 in any one orcombination of FIGS. 1-3, 4A, 4B, 5A, and 10A-10F and/or may, forexample, be taken along line A in any one or combination of FIGS. 4A,4B, and 10A-10F. Figures with a suffix of “B” may, for example,correspond to the SLEG strap cells 104 in any one or combination ofFIGS. 1-3, 4A, 4B, 5B, and 10A-10F and/or may, for example, be takenalong line B in any one or combination of FIGS. 4A, 4B, and 10A-10F.Figures with a suffix of “C” may, for example, correspond to the CGWLstrap cells 106 in any one or combination of FIGS. 1-3, 6A, 6B, 7A, 7B,and 10A-10F and/or may, for example, be taken along line D in any one orcombination of FIGS. 6A, 6B, and 10A-10F. Figures with a suffix of “D”may, for example, correspond to the word-line strap cells 108 in any oneor combination of FIGS. 1-3, 8A, 8B, 9A, 9B, and 10A-10F and/or may, forexample, be taken along line E in any one or combination of FIGS. 8A,8B, and 10A-10F.

As illustrated by the cross-sectional views 1100A-1100D of FIGS.11A-11D, an isolation structure 410 is formed in a substrate 402,demarcating an erase-gate-side device region 402 a and a pair ofword-line-side device regions 402 b. The erase-gate-side device region402 a, the word-line-side device regions 402 b, and the isolationstructure 410 have top layouts as illustrated in any one or combinationof FIGS. 4A, 4B, 6A, 6B, 8A, 8B, and 10A-10F. In some embodiments, aprocess for forming the isolation structure 410 comprises: 1) depositinga pad oxide layer on the substrate 402; 2) depositing a pad nitridelayer on the pad oxide layer; 3) patterning the pad oxide and nitridelayers with a layout of the isolation structure 410; 4) performing anetch into the substrate 402 with the pad oxide and nitride layers inplace to form isolation openings; 5) filling the isolation openings witha dielectric material; and 6) removing the pad oxide and nitride layers.Other processes are, however, amenable.

As illustrated by the cross-sectional views 1200A-1200D of FIGS.12A-12D, a first dielectric layer 1202 and a first conductive layer 1204(also known as a floating gate layer) are formed stacked on thesubstrate 402, between segments of the isolation structure 410. Aprocess for forming the first dielectric layer 1202 and the firstconductive layer 1204 may, for example, comprise: 1) depositing thefirst dielectric layer 1202 on the substrate 402; 2) depositing thefirst conductive layer 1204 on the first dielectric layer 1202 and theisolation structure 410; and 3) performing a planarization into thefirst conductive layer 1204 until the isolation structure 410 isreached. Other processes are, however, amenable. The depositing of thefirst dielectric layer 1202 may, for example, be performed by thermaloxidation and/or some other suitable deposition process(es). Thedepositing of the first conductive layer 1204 may, for example, beperformed by vapor deposition and/or some other suitable depositionprocess(es).

Also illustrated by the cross-sectional views 1200A-1200D of FIGS.12A-12D, a second dielectric layer 1206, a second conductive layer 1208(also known as a control gate layer), and a hard mask layer 1210 areformed stacked over the first conductive layer 1204 and the isolationstructure 410. The second dielectric layer 1206 and the hard mask layer1210 may, for example, be or comprise silicon oxide, silicon nitride,some other suitable dielectric(s), or any combination of the foregoing.In some embodiments, the second dielectric layer 1206 is or comprises anoxide-nitride-oxide (ONO) film and/or the hard mask layer 1210 is orcomprise an ONO film. The second conductive layer 1208 may be orcomprise, for example, doped polysilicon and/or some other suitableconductive material(s).

As illustrated by the cross-sectional views 1300A-1300D of FIGS.13A-13D, a plurality of control-gate stacks 1302 is formed from thesecond dielectric layer 1206 (see FIGS. 12A-12D), the second conductivelayer 1208 (see FIGS. 12A-12D), and the hard mask layer 1210 (see FIGS.12A-12D). The control-gate stacks 1302 comprise individual control-gatedielectric layers 512, individual control gates 406, and individualcontrol-gate hard masks 508. The control gates 406 respectively overliethe control-gate dielectric layers 512, and the control-gate hard masks508 respectively overlie the control gates 406. The control-gate stacks1302 may, for example, have the same top layout as the plurality ofcontrol gates 406 in any one or combination of FIGS. 4A, 4B, 6A, 6B, 8A,8B, and 10B. Other top layouts are, however, amenable.

In some embodiments, a process for forming the control-gate stacks 1302comprises: 1) patterning the hard mask layer 1210 with a control-gatepattern; and 2) performing an etch into the second dielectric layer 1206and the second conductive layer 1208 with the hard mask layer 1210 inplace to transfer the control-gate pattern. Other processes for formingcontrol-gate stacks 1302 are, however, amenable. The patterning may, forexample, be performed by a photolithography/etching process or someother suitable patterning process.

Also illustrated by the cross-sectional views 1300A-1300D of FIGS.13A-13D, control-gate sidewall spacers 514 are formed on sidewalls ofthe control-gate stacks 1302. The control-gate sidewall spacers 514 may,for example, be or comprise silicon oxide, silicon nitride, some othersuitable dielectric(s), or any combination of the foregoing. In someembodiments, the control-gate sidewall spacers 514 are or comprise anONO film. In some embodiments, a process for forming the control-gatesidewall spacers 514 comprises: 1) depositing a sidewall spacer layercovering and lining the control-gate stacks 1302; and 2) performing anetch back into the sidewall spacer layer. Other processes are, however,amenable.

As illustrated by the cross-sectional views 1400A-1400D of FIGS.14A-14D, floating gates 506 and floating-gate dielectric layers 510 areformed respectively from the first conductive layer 1204 (see FIGS.13A-13D) and the first dielectric layer 1202 (see FIGS. 13A-13D). Thefloating gates 506 respectively underlie the control gates 406, and thefloating-gate dielectric layers 510 respectively underlie the floatinggates 506. In some embodiments, a process for forming the floating gates506 and the floating-gate dielectric layers 510 comprises performing anetch into the first conductive layer 1204 and the first dielectric layer1202 using the control-gate sidewall spacers 514 and the control-gatehard masks 508 as a mask. Other processes are, however, amenable.

Also illustrated by the cross-sectional views 1400A-1400D of FIGS.14A-14D, a third dielectric layer 1402 (also known as a gate dielectriclayer) is formed on sidewalls of the control-gate sidewall spacers 514and sidewalls of the floating gates 506. Further, the third dielectriclayer 1402 is formed lining the substrate 402 and the isolationstructure 410 to sides of the control-gate stacks 1302. The thirddielectric layer 1402 defines an erase-gate dielectric layer 516 that isbetween the control-gate stacks 1302 and that will border an erase gate(not yet formed). The third dielectric layer 1402 may be or comprise,for example, silicon oxide and/or some other suitable dielectric(s).

A process for forming the third dielectric layer 1402 may, for example,comprise: 1) depositing a first dielectric portion of the thirddielectric layer 1402 covering and lining the control-gate stacks 1302;2) etching back the first dielectric portion; and 3) depositing a seconddielectric portion of the third dielectric layer 1402 on the substrate402. Other processes are, however, amenable. The first dielectricportion may, for example, be formed by vapor deposition and/or someother suitable deposition process(es), and/or the second dielectricportion may, for example, be formed by thermal oxidation and/or someother suitable deposition process(es).

Also illustrated by the cross-sectional views 1400A-1400D of FIGS.14A-14D, a source line 504 is formed in the substrate 402, between thecontrol-gate stacks 1302. The source line 504 is doped portions of thesubstrate 402 having an opposite doping type as adjoining portions ofthe substrate 402. The source line 504 may, for example, have the toplayout of any one of the source lines 504 in FIG. 10A or some othersuitable top layout. Formation of the source line 504 may, for example,be performed before, during, or after formation of the third dielectriclayer 1402 and/or may, for example, be performed by ion implantationand/or some other suitable doping process(es).

As illustrated by the cross-sectional views 1500A-1500D of FIGS.15A-15D, a third conductive layer 1502 (also known as a gate layer) andan antireflective layer 1504 are formed stacked over and covering thesubstrate 402 and the control-gate stacks 1302. The third conductivelayer 1502 is indented at sides of the control-gate stacks 1302 due tothe change in elevation and may, for example, be or comprise dopedpolysilicon and/or some other suitable conductive material. The thirdconductive layer 1502 may, for example, be or comprise doped polysiliconand/or some other suitable conductive material. The antireflective layer1504 may, for example, be or comprise a bottom antireflective coating(BARC) material and/or some other suitable antireflective material.

As illustrated by the cross-sectional views 1600A-1600D of FIGS.16A-16D, the third conductive layer 1502 and the antireflective layer1504 (see FIGS. 15A-15D) are recessed to below top surfaces of thecontrol-gate stacks 1302, and the antireflective layer 1504 issubsequently removed. The recessing forms an erase gate 408 from thethird conductive layer 1502. The erase gate 408 covers the source line504 and may, for example, have the same top layout as any one of theerase gates 408 in FIGS. 4A, 4B, 6A, 6B, 8A, 8B, and 10B. Other toplayouts are, however, amenable. The recessing may, for example, beperformed by an etch back and/or some other suitable process(es). Theetch back may, for example, comprise: 1) etching the antireflectivelayer 1504 until the third conductive layer 1502 is uncovered; and 2)simultaneously etching the third conductive layer 1502 and theantireflective layer 1504 until the top surface of the third conductivelayer 1502 is recessed to below the top surfaces of the control-gatestacks 1302.

As illustrated by the cross-sectional views 1700A-1700D of FIGS.17A-17D, the third dielectric layer 1402 (see FIGS. 16A-16D) and thethird conductive layer 1502 (see FIGS. 16A-16D) are patterned to formword lines 404 and word-line dielectric layers 518. The word lines 404are formed along sidewalls of the control-gate stacks 1302, and theword-line dielectric layers 518 line the word lines 404. Further, aportion of the erase gate 408 (see FIGS. 16A-16D) is removed from theboundary cell (i.e., FIG. 17A) and the SLEG strap cell (i.e., FIG. 17B).The word lines 404 may, for example, have the same top layout as any oneof the word lines 404 in FIGS. 4A, 4B, 6A, 6B, 8A, 8B, and 10B. Othertop layouts are, however, amenable. The patterning may, for example, beperformed by a photolithography/etching process or some other suitablepatterning process.

As illustrated by the cross-sectional views 1800A-1800D of FIGS.18A-18D, a control-gate hard mask 508 is patterned at the CGWL strapcell (i.e., FIG. 18C) to form a contact opening exposing a pad region602 of a control gate 406. The patterning may, for example, be performedby a photolithography/etching process and/or some other suitablepatterning process(es).

Also illustrated by the cross-sectional views 1800A-1800D of FIGS.18A-18D, source/drain regions 502 are formed in the substrate 402,adjacent to the word lines 404. The source/drain regions 502 may, forexample, be doped regions of the substrate 402 having an opposite dopingtype as adjoining regions of the substrate 402.

Also illustrated by the cross-sectional views 1800A-1800D of FIGS.18A-18D, silicide layers 520 are formed respectively covering the wordlines 404, the erase gate 408, and the source/drain regions 502. Thesilicide layers 520 may, for example, be or comprise nickel silicideand/or some other suitable silicide.

As illustrated by the cross-sectional views 1900A-1900D of FIGS.19A-19D, an interconnect structure 522 is partially formed over the wordlines 404, the erase gate 408, and the control-gate stacks 1302. Theinterconnect structure 522 comprises an inter-layer dielectric (ILD)layer 524 a, and further comprises a first inter-metal dielectric (IMD)layer 524 b overlying the ILD layer 524 a. Further, the interconnectstructure 522 comprises a plurality of first-level wires 120 _(m1) and aplurality of contact vias 122 _(co). The plurality of contact vias 122_(co) and the plurality of first-level wires 120 _(m1) are respectivelyin the ILD layer 524 a and the first IMD layer 524 b, and the contactvias 122 _(co) extend from the first-level wires 120 _(m1) to the strapcells. In some embodiments, the plurality of first-level wires 120 _(m1)comprises a source-line shunt wire 126 at the SLEG strap cell (i.e.,FIG. 19B). The source-line shunt wire 126 may, for example, have a toplayout as illustrated in FIG. 10C.

In some embodiments, a process for partially forming the interconnectstructure 522 comprises: 1) forming the contact vias 122 _(co) by asingle damascene process; and 2) subsequently forming the first-levelwires 120 _(m1) by the single damascene process. Other processes forforming the interconnect structure 522 are, however, amenable. In someembodiments, the single damascene process comprises: 1) depositing adielectric layer (e.g., the ILD layer 524 a or the first IMD layer 524b); 2) patterning the dielectric layer with openings for a single levelof conductive features (e.g., a level of vias or a level of wires); 3)and filling the openings with conductive material to form the singlelevel of conductive features.

As illustrated by the cross-sectional views 2000A-2000D of FIGS.20A-20D, the interconnect structure 522 is expanded. The interconnectstructure 522 comprises a second IMD layer 524 c, a third IMD layer 524d, and a fourth IMD layer 524 e stacked over the first IMD layer 524 b.Further, the interconnect structure 522 comprises a plurality of wiresand a plurality of vias in the second, third, and fourth IMD layers 524b-524 d. A plurality of second-level wires 120 _(m2), a plurality ofthird-level wires 120 _(m3), and a plurality of fourth-level wires 120_(m4) are respectively in the second, third, and fourth IMD layers 524b-524 d. A plurality of first-level vias 122 _(v1) is in the second IMDlayer 524 c and extends from the second-level wires 120 _(m2) to thefirst-level wires 120 _(m1). The plurality of second-level wires 120_(m2) comprises word-line strap lines 118 respectively overlying andelectrically coupled to the word lines 404 by underlying wires and vias.The word-line strap lines 118 may, for example, have top layouts asshown in FIG. 10D or some other suitable top layouts. The plurality ofthird-level wires 120 _(m3) comprises control-gate strap lines 116respectively overlying and electrically coupled to the control gates 406by underlying wires and vias. The control-gate strap lines 116 may, forexample, have top layouts as shown in FIG. 10E or some other suitabletop layouts. The plurality of fourth-level wires 120 _(m4) comprises anerase-gate strap line 114 and a source-line strap line 112 respectivelyoverlying and electrically coupled to the erase gate 408 and the sourceline 504 by underlying wires and vias. The erase-gate strap line 114 andthe source-line strap line 112 may, for example, have top layouts asshown in FIG. 10F or some other suitable top layouts.

In some embodiments, a process for expanding the interconnect structure522 comprises: 1) forming the first-level vias 122 _(v1) and thesecond-level wires 120 _(m2) by a dual damascene process; 2) forming thethird-level wires 120 _(m3) and corresponding vias (not shown) by a dualdamascene process; and 3) forming the fourth-level wires 120 _(m4) andcorresponding vias (not shown) by a dual damascene process. Otherprocesses for expanding the interconnect structure 522 are, however,amenable. In some embodiments, the dual damascene process comprises: 1)depositing a dielectric layer (e.g., the second, third, or fourth IMDlayers 524 b-524 d); 2) patterning the dielectric layer with openingsfor two levels of conductive features (e.g., a level of vias and a levelof wires); 3) and filling the openings with conductive material to formthe two levels of conductive features.

While FIGS. 11A-11D through FIGS. 20A-20D are described with referenceto a method, it will be appreciated that the structures shown in FIGS.11A-11D through FIGS. 20A-20D are not limited to the method but rathermay stand alone separate of the method. Further, while FIGS. 11A-11Dthrough FIGS. 20A-20D are described as a series of acts, it will beappreciated that these acts are not limiting in that the order of theacts can be altered in other embodiments, and the methods disclosed arealso applicable to other structures. In other embodiments, some actsthat are illustrated and/or described may be omitted in whole or inpart.

With reference to FIG. 21, a block diagram 2100 of some embodiments ofthe method of FIGS. 11A-11D through FIGS. 20A-20D is provided.

At 2102, an isolation structure is formed extending into a substrate anddemarcating a device region of the substrate. See, for example, FIGS.11A-11D.

At 2104, a floating gate layer is formed on the device region of thesubstrate. See, for example, FIGS. 12A-12D.

At 2106, a control-gate stack is formed on the floating gate layer andelongated along a control-gate length, where the control-gate stackpartially defines multiple memory cells and multiple strap cells thatare spaced along the control-gate length. See, for example, FIGS.12A-12D through FIGS. 13A-13D.

At 2108, the floating gate layer is patterned to form floating gatesunderlying the control-gate stack. See, for example, FIGS. 14A-14D.

At 2110, a source line is formed in the device region, where the sourceline borders the control-gate stack and is elongated in parallel withthe control-gate stack. See, for example, FIGS. 14A-14D.

At 2112, a gate dielectric layer is formed lining the control-gate stackand the substrate to sides of the control-gate stack. See, for example,FIGS. 14A-14D.

At 2114, a gate layer is formed covering the control-gate stack and thegate dielectric layer. See, for example, FIGS. 15A-15D.

At 2116, the gate layer is recessed until a top surface of the gatelayer is below a top surface of the control-gate stack to form an erasegate that is elongated in parallel with the control-gate stack andoverlies the source line. See, for example, FIGS. 16A-16D.

At 2118, the gate layer is patterned to form a word line that bordersthe control-gate stack on an opposite side of the control-gate stack asthe erase gate and that is elongated in parallel with the control-gatestack and the erase gate. See, for example, FIGS. 17A-17D.

At 2120, a source/drain region is formed in the device region, adjacentto the word line. See, for example, FIGS. 18A-18D.

At 2122, silicide layers are formed on the source/drain region, the wordline, and the erase gate. See, for example, FIGS. 18A-18D.

At 2124, an interconnect structure is formed. The interconnect structurecomprises a word-line strap line, a control-gate strap line, anerase-gate strap line, and a source-line strap line overlying andrespectively electrically coupled to the word line, the control gate,the erase gate, and the source line at the strap cells, where thecontrol-gate strap line is vertically spaced from and is verticallybetween the word-line strap line and the erase-gate strap line. See, forexample, FIGS. 19A-19D through 20A-20D. By vertically spacing thecontrol-gate strap line from the word-line strap line and the erase-gatestrap line, the control-gate strap line, the word-line strap line, andthe erase-gate strap line are in different metallization layers. Thisreduces strap-line density (i.e., strap-line spacing is increased),which allows enhanced scaling (e.g., to process node 40 and beyond)and/or allows use of ELK dielectric materials for IMD layers.

While the block diagram 2100 of FIG. 21 is illustrated and describedherein as a series of acts or events, it will be appreciated that theillustrated ordering of such acts or events is not to be interpreted ina limiting sense. For example, some acts may occur in different ordersand/or concurrently with other acts or events apart from thoseillustrated and/or described herein. Further, not all illustrated actsmay be required to implement one or more aspects or embodiments of thedescription herein, and one or more of the acts depicted herein may becarried out in one or more separate acts and/or phases.

In some embodiments, the present disclosure provides an integrated chipincluding: a memory array including multiple cells in multiple rows andmultiple columns, wherein the cells include multiple first-type strapcells spaced along a first row of the memory array and further includemultiple second-type strap cells spaced along the first row; a word lineand a control gate extending along the first row and partially definingcells of the memory array in the first row; a word-line strap lineextending along the first row at a first elevation above the memoryarray and electrically coupled to the word line at the first- andsecond-type strap cells; and a control-gate strap line extending alongthe first row at a second elevation above the memory array andelectrically coupled to the control gate at the first-type strap cells,but not the second-type strap cells, wherein the first and secondelevations are different. In some embodiments, the word line and thecontrol gate include polysilicon, and wherein the word-line andcontrol-gate strap lines include metal. In some embodiments, the firstelevation is less than the second elevation. In some embodiments, thecells further include multiple third-type strap cells spaced along thefirst row, wherein the integrated chip further includes: an erase gateextending along the first row and partially defining the cells of thememory array in the first row; and an erase-gate strap line extendingalong the first row at a third elevation above the memory array andelectrically coupled to the erase gate at the third-type strap cells,but not the first- and second-type strap cells, wherein the first,second, and third elevations are different. In some embodiments, theintegrated chip further includes: a substrate including a source line,wherein the source line extends along the first row and partiallydefines the cells of the memory array in the first row; and asource-line strap line extending along the first row at the thirdelevation and electrically coupled to the source line at the third-typestrap cells, but not the first- and second-type strap cells. In someembodiments, the cells further include multiple third-type strap cellsspaced along the first row, wherein the integrated chip furtherincludes: a substrate including a source-line region, wherein thesource-line region is elongated along the first row and partiallydefines the cells of the memory array in the first row; and asource-line strap line extending along the first row at a thirdelevation above the memory array and electrically coupled to thesource-line region at the third-type strap cells, but not the first- andsecond-type strap cells, wherein the first, second, and third elevationsare different. In some embodiments, the word-line strap lineelectrically couples to the word line at multiple first locations thatrepeat along the first row with a first frequency, wherein thesource-line strap line electrically couples with the source-line regionat multiple second locations that are repeat along the first row with asecond frequency, and wherein the first frequency is greater than and isan integer multiple of the second frequency. In some embodiments, thecells include multiple memory cells spaced along a first column of thememory array, wherein the integrated chip further includes: a bit lineextending along the first column at a third elevation above the memoryarray and electrically coupled to the memory cells, wherein the first,second, and third elevations are different.

In some embodiments, the present disclosure provides another integratedchip including: a memory array including a plurality of cells in aplurality of rows and a plurality of columns, wherein the plurality ofrows includes a first row; an erase gate and a control gate elongatedalong the first row, wherein the erase and control gates partiallydefine cells of the memory array in the first row; an erase-gate strapline elongated along the first row at a first elevation above the memoryarray, wherein the erase-gate strap line is electrically coupled to theerase gate at a plurality of first locations along the first row; and acontrol-gate strap line elongated along the first row at a secondelevation above the memory array that is different than the firstelevation, wherein the control-gate strap line is electrically coupledto the control gate at a plurality of second locations along the firstrow. In some embodiments, the first elevation is greater than the secondelevation. In some embodiments, the first locations are evenly spacedalong the first row and have a first pitch, wherein the second locationsare evenly spaced along the first row and have a second pitch less thanthe first pitch. In some embodiments, the integrated chip furtherincludes: a substrate including a source line, wherein the source lineis elongated along the first row and partially defines the cells of thememory array in the first row; and a source-line strap line elongatedalong the first row at a third elevation above the memory array that isdifferent than the second elevation, and wherein the source-line strapline is electrically coupled to the source line at a plurality of thirdlocations along the first row. In some embodiments, the first locationsare spaced along the first row and have a first pitch, wherein the thirdlocations are spaced along the first row and have the first pitch. Insome embodiments, the first and third elevations are the same. In someembodiments, the integrated chip further includes: a word line elongatedalong the first row and partially defining the cells of the memory arrayin the first row; and a word-line strap line elongated along the firstrow at a third elevation above the memory array that is different thanthe first and second elevations, wherein the word-line strap line iselectrically coupled to the word line at a plurality of third locationsalong the first row.

In some embodiments, the present disclosure provides a method forforming an integrated chip, the method including: forming a control gateelongated along a control-gate length, wherein the control gatepartially defines multiple memory cells and multiple first-type strapcells that are spaced along the control-gate length; depositing a gatelayer covering the control gate; patterning the gate layer to form aword line and an erase gate that are elongated in parallel with thecontrol gate and partially define the memory cells and the first-typestrap cells, wherein the control gate is between and borders the wordline and the erase gate; and forming multiple control-gate contact viasand multiple word-line contact vias respectively on the control gate andthe word line, wherein the control-gate and word-line contact vias areat the first-type strap cells, but not the memory cells. In someembodiments, the control gate is formed with multiple pad regionsrespectively at the first-type strap cells, but not at the memory cells,wherein the pad regions protrude in a direction transverse to thecontrol-gate length, and wherein the control-gate contact vias are onthe control gate respectively at the pad regions. In some embodiments,the control gate, the word line, and the erase gate partially definemultiple second-type strap cells that are spaced along the control-gatelength, wherein the method further includes: doping a substrate to forma source line that is elongated in parallel with the control gate,wherein the erase gate is formed overlying the source line and hasdiscontinuities respectively at the second-type strap cells; and formingmultiple source-line contact vias on the source line and respectively atthe second-type strap cells, but not the memory cells and the first-typestrap cells. In some embodiments, the method further includes formingmultiple pairs of erase-gate contact vias on the erase gate, wherein thepairs are respectively at the second-type strap cells, but not thememory cells and the first-type strap cells, and wherein the erase-gatecontact vias for each of the pairs are respectively on opposite sides ofa corresponding one of the discontinuities and are along opposingsidewalls of the erase gate at the corresponding one of thediscontinuities. In some embodiments, the method further includes:forming an interconnect structure over the word line and the controlgate, wherein the interconnect structure includes a word-line strap lineelongated in parallel with the word line and electrically coupled to theword line through the word-line contact vias; depositing an IMD layerover the interconnect structure; patterning the IMD layer to form atrench elongated in parallel with the control gate; and filling thetrench with a conductive material to form a control-gate strap lineelectrically coupled to the control gate through the interconnectstructure, wherein the interconnect structure is electrically coupled tothe control gate through the control-gate contact vias.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. An integrated chip comprising: a memory array comprising multiple cells in multiple rows and multiple columns, wherein the cells comprise multiple first-type strap cells spaced along a first row of the memory array and further comprise multiple second-type strap cells spaced along the first row; a word line and a control gate extending along the first row and partially defining cells of the memory array in the first row; a word-line strap line extending along the first row at a first elevation above the memory array and electrically coupled to the word line at the first- and second-type strap cells; and a control-gate strap line extending along the first row at a second elevation above the memory array and electrically coupled to the control gate at the first-type strap cells, but not the second-type strap cells, wherein the first and second elevations are different.
 2. The integrated chip according to claim 1, wherein the word line and the control gate comprise polysilicon, and wherein the word-line and control-gate strap lines comprise metal.
 3. The integrated chip according to claim 1, wherein the first elevation is less than the second elevation.
 4. The integrated chip according to claim 1, wherein the cells further comprise multiple third-type strap cells spaced along the first row, and wherein the integrated chip further comprises: an erase gate extending along the first row and partially defining the cells of the memory array in the first row; and an erase-gate strap line extending along the first row at a third elevation above the memory array and electrically coupled to the erase gate at the third-type strap cells, but not the first- and second-type strap cells, wherein the first, second, and third elevations are different.
 5. The integrated chip according to claim 1, wherein the cells further comprise multiple third-type strap cells spaced along the first row, and wherein the integrated chip further comprises: a substrate comprising a source-line region, wherein the source-line region is elongated along the first row and partially defines the cells of the memory array in the first row; and a source-line strap line extending along the first row at a third elevation above the memory array and electrically coupled to the source-line region at the third-type strap cells, but not the first- and second-type strap cells, wherein the first, second, and third elevations are different.
 6. The integrated chip according to claim 5, wherein the word-line strap line electrically couples to the word line at multiple first locations that repeat along the first row with a first frequency, wherein the source-line strap line electrically couples with the source-line region at multiple second locations that are repeat along the first row with a second frequency, and wherein the first frequency is greater than and is an integer multiple of the second frequency.
 7. The integrated chip according to claim 1, wherein the cells comprise multiple memory cells spaced along a first column of the memory array, and wherein the integrated chip further comprises: a bit line extending along the first column at a third elevation above the memory array and electrically coupled to the memory cells, wherein the first, second, and third elevations are different.
 8. A method for forming an integrated chip, the method comprising: forming a control gate elongated along a control-gate length, wherein the control gate partially defines multiple memory cells and multiple first-type strap cells that are spaced along the control-gate length; depositing a gate layer covering the control gate; patterning the gate layer to form a word line and an erase gate that are elongated in parallel with the control gate and partially define the memory cells and the first-type strap cells, wherein the control gate is between and borders the word line and the erase gate; and forming multiple control-gate contact vias and multiple word-line contact vias respectively on the control gate and the word line, wherein the control-gate and word-line contact vias are at the first-type strap cells, but not the memory cells.
 9. The method according to claim 8, wherein the control gate is formed with multiple pad regions respectively at the first-type strap cells, but not at the memory cells, wherein the pad regions protrude in a direction transverse to the control-gate length, and wherein the control-gate contact vias are on the control gate respectively at the pad regions.
 10. The method according to claim 8, wherein the control gate, the word line, and the erase gate partially define multiple second-type strap cells that are spaced along the control-gate length, and wherein the method further comprises: doping a substrate to form a source line that is elongated in parallel with the control gate, wherein the erase gate is formed overlying the source line and has discontinuities respectively at the second-type strap cells; and forming multiple source-line contact vias on the source line and respectively at the second-type strap cells, but not the memory cells and the first-type strap cells.
 11. The method according to claim 10, further comprising: forming multiple pairs of erase-gate contact vias on the erase gate, wherein the pairs are respectively at the second-type strap cells, but not the memory cells and the first-type strap cells, and wherein the erase-gate contact vias for each of the pairs are respectively on opposite sides of a corresponding one of the discontinuities and are along opposing sidewalls of the erase gate at the corresponding one of the discontinuities.
 12. The method according to claim 8, further comprising: forming an interconnect structure over the word line and the control gate, wherein the interconnect structure comprises a word-line strap line elongated in parallel with the word line and electrically coupled to the word line through the word-line contact vias; depositing an inter-metal dielectric (IMD) layer over the interconnect structure; patterning the IMD layer to form a trench elongated in parallel with the control gate; and filling the trench with a conductive material to form a control-gate strap line electrically coupled to the control gate through the interconnect structure, wherein the interconnect structure is electrically coupled to the control gate through the control-gate contact vias.
 13. The integrated chip according to claim 1, further comprising: a plurality of first contact vias overlying and directly contacting the word line, wherein the first contact vias repeat along the word line with a first frequency, and wherein the word-line strap line electrically couples to the word line through the first contact vias; and a plurality of second contact vias overlying and directly contacting the control gate, wherein the second contact vias repeat along the control gate with a second frequency less than the first frequency, and wherein the control-gate strap line electrically couples to the control gate through the second contact vias.
 14. An integrated chip comprising: a memory array comprising multiple cells in multiple rows and multiple columns, wherein the multiple cells comprise multiple first-type strap cells spaced along a first row of the memory array and a second row of the memory array; a pair of word lines, a pair of control gates, and an erase gate elongated in parallel with the first and second rows and partially defining cells of the memory array in the first and second rows, wherein the control gates are between and respectively border the word lines, and wherein the erase gate is between and borders the control gates; and a plurality of first contact vias respectively overlying and electrically coupled to the word lines and the control gates, wherein the first contact vias have a first contact-via pattern that overlies the word lines and the control gates and that repeats along the first and second rows at each of the first-type strap cells.
 15. The integrated chip according to claim 14, wherein the first contact-via pattern includes a pair of word-line contact vias and a pair of control-gate contact vias, wherein the word-line contact vias respectively overlie the word lines and are oriented along a first diagonal axis, and wherein the control-gate contact vias respectively overlie the control gates and are oriented along a second diagonal axis that crosses the first diagonal axis.
 16. The integrated chip according to claim 14, wherein the multiple cells comprise multiple second-type strap cells spaced along the first and second rows, wherein the integrated chip further comprises: a plurality of second contact vias respectively overlying and electrically coupled to the word lines, wherein the second contact vias have a second contact-via pattern different than the first contact-via pattern that overlies the word lines and that repeats along the first and second rows at each of the second-type strap cells.
 17. The integrated chip according to claim 14, wherein the multiple first-type strap cells repeat along the first and second rows with a first frequency, wherein the multiple cells comprise multiple second-type strap cells spaced along the first and second rows and repeating along the first and second rows with the first frequency, and wherein the first-type and second-type strap cells have different top layouts.
 18. The integrated chip according to claim 14, further comprising: a pair of word-line strap lines extending respectively along the first and second rows at a first elevation above the memory array and electrically coupled respectively to the word lines at each of the first-type strap cells; and a pair of control-gate strap lines extending respectively along the first and second rows at a second elevation above the memory array and electrically coupled respectively to the control gates at each of the first-type strap cells, wherein the second elevation is greater than the first elevation.
 19. The integrated chip according to claim 14, wherein the multiple cells comprise multiple second-type strap cells spaced along the first and second rows, and wherein the integrated chip further comprises: a pair of word-line strap lines extending respectively along the first and second rows and electrically coupled respectively to the word lines at each of the first-type and second-type strap cells; and a pair of control-gate strap lines extending respectively along the first and second rows and electrically coupled respectively to the control gates at each of the first-type strap cells but not the second-type strap cells.
 20. The integrated chip according to claim 14, wherein the cells comprise multiple memory cells spaced along a first column of the memory array, and wherein the integrated chip further comprises: a bit line extending along the first column at a first elevation above the memory array and electrically coupled to the memory cells; a pair of word-line strap lines extending respectively along the first and second rows at a second elevation above the memory array and electrically coupled respectively to the word lines at each of the first-type strap cells; and a via extending from the first elevation to the second elevation. 